This invention relates to a gray level compensation for a picture recorder or a density level, compensation for the image recording apparatus, and in particular, to a gray level compensator aiming to prevent fluctuation of a gray level of a recorded picture according to the change of the various factors related to picture recording.
With respect to a picture recorder, a photo scanning recorder is known wherein the light beam is modulated according to the picture signal, the modulated light beam is made to scan the photosensitive material (recording medium) and the photosensitive material exposed thereby is developed (see Japanese Patent Application Laid-open NO.54-42243 and NO.59-83150).
An embodiment of the said photo scanning recorder will be described with reference to FIG. 17. Light beam (laser beam) 2 emitted from semiconductor laser 1 is made into the parallel beam by the collimator lens 3, and is reflected by mirror 4. Then it enters light deflector 5 such as a rotary polygon mirror. Light beam 2 is reflected and deflected by said light deflector and is led into the convergent lens 6, through which it scans the photosensitive material in the direction approximately at a right angle to the arrowed Y-direction (main scanning). At the same time, the photo sensitive material 7 is transferred in the said arrowed Y-direction by the, transfer unit not illustrated in the said FIG. 17, and is scanned (sub-scanning), whereby light beam 2 is irradiated on the photo sensitive material 7 two-dimensionally.
Said light beam 2 is modulated according to the picture signal output from the picture signal output device, and the picture carried by the said picture signal is recorded as photographic latent image on said photo sensitive material 7 when exposed by this modulated light beam.
Referring to FIG. 18, the picture signal is a digital signal, and is led into the signal conversion circuit 9 via the picture memory 8, as shown in FIG. 18: where it is converted into a light modulation signal, which, in turn, is converted into analog signal by the digital-to-analog converter 11 after passing through the latch circuit 10. The said analog light modulation signal enters the light modulation circuit 12, which modulates the laser beam emitted from said semiconductor laser 1. The said modulated laser beam scans the photo sensitive material (film) 7, and the picture image is thereby recorded as a photographic latent image.
Furthermore, the exposed photo sensitive material 7 is sent to the known development processor 13, where said photo sensitive material is subjected to development, fixing, water-washing and drying. Through this process, the said photographic latent image is developed, and the picture image carried by the said image signal is recorded on the photo sensitive material 7 as a visible image.
The semiconductor laser 1 is directly modulation-driven in the said light modulation circuit 12. When the gas laser is used as a light source, intensity modulator including the acousto-optical modulation element (AOM) is normally employed.